1. Field of the Present Invention
The present invention concerns a photothermographic material and an image forming method by using the photothermographic material.
2. Description of the Related Art
In recent years, there has been a strong desire to decrease the volume of processing liquid wastes in the medical field from the view point of environmental protection and economy of space. In the field of medical diagnosis, photothermographic materials have been proposed. To use photosensitive photothermographic materials in medical diagnoses and photographic techniques, they must be capable of being exposed efficiently by laser image setters or laser imagers. Additionally, they must be capable of forming clear black images having high resolution and sharpness. With photosensitive photothermographic materials, thermal development processing systems can be supplied to customers that obviate the need for solution system processing chemicals, have a simple construction and are environmentally safe.
While such requirements also exist in the field of general imaging, images for medical use particularly require high image quality of excellent sharpness and graininess since delicate imaging characteristics is needed. Further, images of blue black image tone are preferred to facilitate easy diagnosis. At present, various kinds of hard copy systems that utilize pigments and dyes such as ink jet printers or electrophotography have been marketed as conventional image forming systems, but they are not satisfactory as image output systems for medical use.
Thermal image forming systems utilizing organic silver salts are described in the art. In general, a photothermographic material typically has an image forming layer and the image forming layer contains a catalytically active amount of photocatalyst (for example, silver halide), a reducing agent, a reducible silver salt (for example, organic silver salt) and, optionally, a color toning agent for controlling the color tone of silver dispersed in a binder matrix. The photothermographic material, when heated to a high temperature (for example, 80° C. or higher) after imagewise exposure, forms black silver images by oxidation/reduction reaction between a silver halide or reducible silver salt (functioning as an oxidizer) and a reducing agent. The oxidation/reduction reaction is promoted by the catalytic effect of latent images of the silver halide formed by exposure. Accordingly, black silver images are formed in an exposed region. Fuji Medical Dry Imager FM-DPL has been sold as a medical image forming system using photothermographic materials.
In photothermographic materials, it is a goal to provide the photosensitive material with a property to ease sliding of the material and thus improve the transportability during production and fabrication and accumulation property thereof. Suggested materials include liquid paraffin described in JP-A No. 10-69023, liquid lubricant such as silicone oil described in JP-A No. 2001-5138 and solid esters such as carnauba wax described in JP-A Nos. 2000-112062 and 2001-5137. Such materials for easing sliding of a photothermographic imaging material are known as “slipping agents” and are used preferably for the protection layer on the side of emulsion layer or the protection layer on the side of back surface and, particularly, they are generally used for the outermost layer.
However, the outermost layer is a portion in direct contact with a transportation apparatus, and accumulated material sometimes causes transportation failure and, further, can have undesired effects on the output images. Since they may also possibly cause failures in the plane of the photosensitive materials, selection of a material to ease sliding of the photothermographic material (“slipping agent”) as an additive is an important subject. Accordingly, there is a need in the art for the development of improved slipping agents to ease sliding of photothermographic materials and development of photothermographic materials with such additives.